Brace Height.
This is the distance between your bowstring and the back of the bow (the portion facing away from you) or the Belly (the portion facing you) the manufacturer will specify a measurement in Inches from say 7-8 inches---8-8 3/4 Inches etc. These measurements are the range your bow is designed to be shot safely within. Finding the perfect brace height is down to the Archer, and it's simple to do, essential to learn.
You adjust the Brace height by twisting (tightening) your string to make it higher, untwisting to make it lower. It goes without saying that your string should be well waxed. Start with your bow set at the lowest brace height as recommended by the manufacturer, and gradually twist it till it raises by 1/4 Inch increments. Shoot some arrows at every interval, and as you continue to shoot (raising your brace height) you will find a spot where the bow becomes quieter and smoother to shoot, this is your perfect brace height. Note down the measurement and now you can be sure your bow is always perfectly braced
Too low a brace height and you run the risk of hitiing your forearm if your technique is not solid, the bow is noisier as well. Too high a brace height and you run the risk of over straining your bow limbs, especially on Wooden bows.